Inspection systems for the analysis of moving web materials have proven critical to modern manufacturing operations. Industries as varied as metal fabrication, paper, non-woven materials, and films rely on these inspection systems for both product certification and online process monitoring.
Products created on web process lines are subject to anomalies or defects from many sources. One particular concern is web line-induced anomalies, such as those created by continuously rotating equipment contacting the web in a regular, repeating pattern. Such equipment can generally be described as a “roll.” Typical rolls utilized within a web manufacturing line include but are not limited to casting wheels, pull rolls, nip rolls, microreplicating rolls, web cleaning components, and idlers.
For example, the surface of a roll may be damaged (e.g., scratched) or a may have a contaminant (e.g., dirt or other particle) that induces an anomaly or defect in the moving web carried by the roll. Moreover, the roll can cause so-called “repeating anomalies” in that a new anomaly may be imparted into the moving web with each rotation of the roll. On the resulting web product, these anomalies repeat at a distance equal to the roll's circumference in the same cross-direction or “cross-web” position. Web process lines may have hundreds of rolls, many of which may have similar diameters. Identifying the specific offending roll that induced a repeating anomaly or defect within the web can be difficult with conventional inspection systems.
For example, commercially available web inspection systems provide identification of repeating defects, including cross-web position and down-web repeat distance. However, these systems typically require a priori knowledge of existing roll diameters on a given process line in order to extract repeating defect information from the entire data stream. Moreover, in many cases there may be many idlers or other rolls within a given web process line with circumferences that are near a given repeat distance of a repeating anomaly, making defect-causing roll identification difficult. As one example, a length orienter on a film making line may have numerous rolls (e.g., twelve or more), all of nominally the same eight-inch diameter. It is often difficult to determine the unique defect-causing roll using traditional methods due in part to slight variations in diameter of each of these rolls. In addition, conventional systems are often unable to account for any spatial distortion (e.g., stretching) of the web between the defect-causing roll and the web inspection system. Further, undocumented roll changes to a web process line can also occur. For example, a six-inch diameter roll may be replaced by a five-inch diameter roll and may begin introducing repeat defects. Process operators using conventional web inspection systems might not check the changed roll as the source of anomalies or defects due to the change not being documented and the assumed diameter of the roll being incorrect.